This invention relates to a speed-light, or electronic flash, equipped with a calculating device. It is known in the prior art to provide an electronic flash with a device for calculating a combination of an aperture value and a film-to-subject distance in relation to sensitivity of a photographic film loaded in a camera. THis calculating device, as is well known, is to indicate a combination of the above-mentioned aperture value and the film-to-subject distance on the basis of a computation formula for an exposure guide number (G.N.), i.e., ##EQU1## (where Sx denotes an arbitrary film sensitivity; Sa represents a reference film sensitivity; A is an aperture value; and D is a distance of film to a photographic object).
Heretofore, most of the calculator calculators of this sort have been mounted on the upper, rear, or side surfaces of the speed-light or electronic flash, and their design has also been mostly of a flat disc shape (with graduations being made on the flat surface of a rotational disc). Such calculating devices are inferior in their operability because an operator cannot properly place his (or her) finger on the device. Also, they have the disadvantage that, when the calculator is mounted on the camera, viewing positions of both camera view-finder and calculator are so separated that viewing operations are difficult.
Further, with the conventional calculating devices with the setting of the film sensitivity graduation of the calculating device is performed separately from the setting of the film sensitivity dial of a camera provided with a light metering circuit. The setting operations are rather complicated, with the consequence that, when the film sensitivity graduation as set in the calculator differs from that as set on the sensitivity setting dial of the camera, an error in exposure results when performing flash photography in accordance with indication on the calculator.